The invention is useful for sealing the passage of a drive shaft from a motor compartment to a hydraulic unit in submersible pumps and mixers, etc., albeit other use is conceivable. The submersible pumps and mixers typically comprise an electrically driven motor and a hydraulic unit comprising an impeller/propeller connected to the motor compartment via a drive shaft. In order to prevent medium in the hydraulic unit from entering into the motor along the drive shaft, seal devices are arranged between the hydraulic unit and the motor compartment. A common type of seal device is an axial face seal, also known as a mechanical face seal, comprising a seal member rotating with the drive shaft and abutting/sealing against a stationary seal member which is attached to a housing wall forming part of the motor compartment. The two seal members are pressed towards each other by spring force to prevent medium from entering the sealing interface.
In submersible pumps, for example, a set of two axial face seal assemblies are often installed to provide sealing interfaces at the passages of the drive shaft reaching through a fluid filled housing portion which defines a barrier for the pumped medium, between the motor compartment and the hydraulic unit.
The axial face seal assemblies which are referred to generally comprise a ring-shaped seal member presenting a sealing end face, which is axially movable in relation to a base element of the axial face seal assembly. The seal member is biased towards the stationary seal member on the housing wall by means of a spring, which is supported from the base element. The base element is connectable to the drive shaft for joint movement therewith, i.e. the base element is non-rotatably connectable to the drive shaft at an axially fixed position. The seal member and the base element are likewise non-rotatably connected in relation to each other. Thus, the axial face seal assembly is supported on the drive shaft for joint rotation therewith, and in concentric relation with the drive shaft.
PCT/SE2009/000132, which is incorporated by reference, discloses an axial face seal assembly which comprises a carrier in which the seal member is seated. The carrier comprises three dowels which extend into corresponding dowel holes of the base element, i.e. the dowels functions as torque driver pins and transmits the rotational movement of the drive shaft/base element to the moving part, i.e. the carrier/seal member. However, when the axial face seal assembly is mounted in a submersible pump, suitable for pumping contaminated liquid, it will experience relative movement between the base element and the carrier in the axial direction due to thermal expansion, vibrations, obliquity, etc. In course of time each dowel and dowel hole will wear on each other, i.e. the dowel will tear a slot in the corresponding dowel hole at the torque transmitting interface and the dowel hole will wear on the side of the dowel facing the torque transmitting interface. As a result said side of the dowel will be rough and irregular and the upper edge of the dowel hole may get caught on any undesired irregularity on the dowel. In addition, the dowel may become wedged in the slot in the dowel hole. Thus, the wear will obstruct the axial movement of the carrier/seal member in relation to the base element. As a result the axial face seal assembly will often cause the axial face seal to become overloaded and break or become opened and leak. When the pumped liquid comprises abrasive matter, the working life of the axial face seal assembly will be substantially reduced, since the abrasive matter will function as an abrasive between the dowel and the dowel hole.